For me, this happens most often when I'm painting, and I justify it by reminding myself there's already a saying about how boring it is to watch the stuff dry. Then I think about how much better things look when you take your time.
Haste, as they say, makes waste. If you do one heavy, gloopy round of spray paint, you'll have compromised the project right out of the gate. If you don't give a wall's first coat of paint time to dry before coming back with the second, you'll have to take even more steps to get a smooth finish. The list goes on! Pass the active project time with the help of NPR or some music. Distract yourself between steps with other tasks, a snack break, or even by getting out of the house.
Haste also makes for expletives. Going at an unhurried pace will make the whole experience more enjoyable. If you're, say, assembling furniture but rushing through the directions, you may very well end up banging on that Ikea storage unit and berating the little wordless Ikea directions man (not that I would know anything about that). As much as you want to get it put together, step away from the HELMER as soon as you start to feel frustrated. You'll be able to come back with a clearer head for what you missed and won't have wasted your time or energy.
Does this happen to you, and what helps you get past it?
Image: My Colortopia